Such a knife is known from DE 197 23 279 [U.S. Pat. No. 6,148,520]. A blade support is mounted for shifting in the housing between a position retracted into and a position projecting from the housing. In the forward position the blade projects from the housing. An operating part has a primary coupling element that can be engaged with and disengaged from a secondary coupling element of the blade support in order to move the blade support from the retracted position into the projecting position.
Forward movement of the operating part is limited. With regard to this frontmost position of the operating part the blade support is allowed an additional relative movement by means of which the primary and the secondary coupling element may be disengaged from each other. The blade support may therefore be retracted back into the housing via a spring with decreasing cutting force on the blade.